Recently, hole-type optical filters in which apertures are periodically arranged in arrays on a metallic thin film and which perform wavelength selection utilizing surface plasmons have been proposed in Patent Document 1 and Non-Patent Document 1.
Conventionally, although also depending on the film thickness, the transmittance of a metallic thin film including an aperture diameter of a size that is less than or equal to a light wavelength is considered to be less than approximately 1%.
However, as described in Patent Document 1, when apertures of a predetermined size are arrayed on a metallic thin film at a period that is consistent with the wavelength of plasmons, the transmittance of light of a wavelength that induces surface plasmons is significantly enhanced.
Further, Non-Patent Document 1 teaches that transmission spectra of RGB can be obtained using this kind of hole-type optical filter that utilizes surface plasmons. More specifically, Non-Patent Document 1 discloses that transmission spectra having wavelengths of 436 nm (blue), 538 nm (green), and 627 nm (red) were obtained using a metallic thin film having subwavelength aperture arrays.
Patent Document 2 discloses a wavelength filter which utilizes a surface plasmon.    (Patent Document 1) U.S. Pat. No. 5,973,316    (Patent Document 2) WO2002/008810    (Non-Patent Document 1) Nature Vol. 424, 14 Aug., 2003 (FIG. 4)